(1) Field of the Invention
This invention relates to earth working, and more particularly to agricultural tillage. Farmers have ordinary skill in the art to which this invention relates.
(2) Description of the Related Art
For many years, farm tractors have been used to draft tillage equipment, and particularly heavy tillage equipment, through fields. By heavy tillage equipment, it is meant tillage equipment that tills the soil deeply, e.g., over 3". Besides turning plows and rippers, listers are common type of such equipment.
Because agricultural development in the United States and the increased labor costs, extremely large tractors are used so that only one farmer can till large areas of land. As used herein, a large tractor means a tractor having over 45 horse power. At a time when labor costs were less, it was economically feasible to use small tractors. Now, the use of smaller tractors is prohibitively expensive because each tractor requires a human operator. Therefore, for many years, the trend in U.S. agriculture has been to use larger and larger tractors. The tool bars are long and equipped with gauge wheels. A wide strip or swath of ground is tilled with each pass of the tractor.
Typically, these large tractors have low pressure pneumatic tires. As the power of the tractor increases, it is necessary to increase the weight for sufficient traction upon the soil to draft the heavy tillage equipment through the earth. To prevent undue compaction of the ground under the wheels, extremely large tires with low air pressure are used to distribute the weight of the tractor over a large area.
However, large tires with low air pressure results in a lack of lateral stability. The frame of the tractor tends to movebback and forth laterally even though the tread of the tires follows the earth faithfully. The tires themselves permit the wheels, and thus the frames, to move laterally.
Farmers have always had difficultly plowing straight furrows. Surface indentation, rocks, clods, clumps of weeds, grasses and roots, steering corrections, and other causes of lateral shifts, jumps, jerks, and wiggles the implement seems uncorrectable with prior art equipment. In fact, a lateral sway was designed into the hitch (Morling, pages 7 and 11). (Roy W. Morling, Agricultural Tractor Hitches Analysis of Design Requirements, No. 5, Dec. 12, 1979, published by ASAE, P.O. Box 410, St. Joseph, Mich. 49085) A copy of this publication is available in the Patent Office file of our prior patent application, Ser. No. 07/925,162. The soft tires tend to aggravate the problem. Also, with long tool bars, plows on one end may be plowing in hard soil while plows on the other end are plowing in soft soil.
It has long been known in the design of draft vehicles, such as farm tractors, that the equipment might be drafted from the frame of the tractor forward of the rear axles. Examples of such drafting apparatus include the French patent to GUILLOTTE, Pat. No. 1,098,133, "publie" July 18, 1955 or the U.S. Patent to SILVER ET AL, 2,713,295. Also, see page 4 of Morling. Although the drafting from this position seems advantageous, applicants have difficulty explaining why this advantageous result came about. The only publication they found that seemed to discuss the problem was Morling and the publication by Gill and Berg, "Soil Dynamics in Tillage and Traction" by William R. Gill and Glen E. Vanden Berg, a publication of the Agricultural Research Service of the United States Department of Agriculture, United States Printing Office, 1967. Pages 340-42, 364-365, 416-421, and 511 of this publication are available in the Patent Office file of our prior patent application, Ser. No. 07/925,162. Applicants have provided the highlighting.
Gill and Berg indicate at page 340 the efficiency of power transmission from the rear axle through the tires into tilled or agricultural soil is perhaps no better than 50 percent (as applicants understand the discussion).
About 1950, the great advantages of the three point hitches were commercially recognized. Three point hitches are shown in the U.S. Pats. issued to DOSS, U.S. Pat. No. 4,142,588, Mar. 6, 1979; ALTGELT, U.S. Pat. No. 2,637,262, May 5, 1953; and ANDERSON, U.S. Pat. No. 2,797,627, July 2, 1957, for example. These three point hitches have the great advantage of providing quick attachment and detachment of implements to farm tractors. The three point hitch made it possible for one man to quickly detach one implement and attach another. Also, see page 6 of Morling. Because of the great advantages of the three point hitch, tractor manufacturers quit manufacturing tractors with equipment drafted from the frame forward of the rear axle. Many three point hitches include forces sensing and load control features. Morling concludes that these features are not economically beneficial for large tractors (pages 17, 18, and 27). Energy losses are explained on page 18.
In recent years, quick couplers or quick hitch frames have become widely used. (Morling, page 21) The quick hitch frame is a yoke or frame which is attached to the ends of the links of the three point hitch. The rear of the yoke or frame contains hooks which may readily be hooked onto horizontal bolts and pins by which the agricultural implements would otherwise be hooked to the distal points of the three links.
Farm tractors or tractors for agricultural use are normally not single use vehicles. Although it has been described as primarily being used to draft heavy tillage equipment, it will also be understood that at various times they are used to draft equipment requiring a power takeoff shaft from the engine of the tractor to the towed implement. In addition to this, often times, the towed implement will be connected by a trailer hitch or the trailer itself might be connected.
The design of the tractors is such that the power takeoff and trailer hitch sometimes would interfere with the cross bracing of the hitch as shown in the application of Ser. No. 06/925,162 indicated above.
The rear three point hitch tends to lift the front of the tractor off the ground during certain conditions. It was often sought to correct this problem by use of counterweights at the front of the tractor.
RUDD, U.S. Pat. No. 3,749,421, issued June 31, 1973, discloses arms which extend from bearings on the rotating axle outboard of the rear large tractor tires. These are connected to a tool bar or an elongated draw bar. The tractor lift arms are connected to the draw bar by pivot blocks 54.
The following patents are of record in the parent application (some are discussed above).
______________________________________ United States Patents MCCALL 984,581 PLUM 1,608,666 HESTER 2,019,854 THEIS 2,197,670 WATSON 2,496,760 ALTGELT 2,637,262 SILVER ET AL 2,713,295 RUDIO 2,752,838 ANDERSON 2,797,627 NEEDHAM 3,021,621 STEFFE 3,601,202 RUDD 3,749,421 CAPEHART 3,840,076 QUANBECK 4,068,723 BUCK ET AL 4,069,874 LARSON 4,117,889 DOSS 4,142,588 WILLIAMS 4,331,345 French Patent GUILLOTTE 1,098,133 ______________________________________
These patents are considered pertinent because the applicant believes the Examiner would consider anything relevant or pertinent to the parent application to be relevant to the examination of this application.